1. Field of the Invention
The present invention relates to a high-frequency power amplifier circuit and a high-frequency power amplifier module which are used in a micro-wave communication devices, etc.
2. Description of the Prior Art
In recent years the communication technology involving high frequencies has been progressing, and handy communication devices using high frequencies are proliferating rapidly. Accordingly, miniaturization of the handy communication devices is being longed for.
Conventionally, high-frequency power amplifier modules are in much use where a field effect transistor (hereinafter referred to as FET) is used in the high-frequency power amplifier part for such handy high-frequency communication devices.
The above-described high-frequency power amplifier module has become commercially available as a module where a high-frequency power amplifier circuit is formed on a ceramic substrate having an area for example of around 10 mm by 10 mm. As a module circuit of this kind, the high-frequency power amplifier circuit as shown in FIG. 2 is generally used. That circuit consists of an input matching circuit 23 provided between the signal input terminal 21 and the gate of FET 22, an output matching circuit 24 which is provided between the drain of FET 22 and the output terminal 27, and a drain bias circuit 25 of FET 22, etc.
However, with the above-described high-frequency power amplifier circuit there was a problem that the frequency component of an input signal together with its higher harmonic component is supplied to the gate of FET 22 so that the waveform of the output signal would have become distorted and thus its performance would not be stable.
For the purpose of solving this problem, as for the high-frequency power amplifier circuit disclosed in Japanese Patent Application Laid-Open No. 9-162657, a high-frequency power amplifier circuit suppressing an occurrence of distortion is proposed by way of short-circuiting only the second higher harmonic component of frequency in the input signal which affects the distortion much with the following configurations to be added.
(1) A transmission line having a length of approximately one eighth of the wavelength of an input signal with one end getting opened is to be connected to the gate of FET.
(2) A transmission line having a length of approximately a quarter of the wavelength of an input signal with one end getting harmonically grounded is to be connected to the gate of FET.
(3) one end of a series resonance circuit comprising an inductor and a capacitor in series together with the resonance frequency being approximately twice as that of the input signals are to be connected to the gate of FET. Furthermore, the other end of that series resonance circuit is to be grounded.
(4) A first transmission line and a second transmission line with respective one ends getting opened are to be connected to the gate of FET. Furthermore, either the first transmission line or second transmission line has a length of approximately one eighth of the wavelength of an input signal having a frequency at a lowest limit and the other has a length of approximately one eighth of the wavelength of an input signal having a frequency at an uppermost limit.
(5) One end each of a first as well as a second transmission line is harmonically grounded at the gate of FET. Furthermore, either the first transmission line or second transmission line has a length of approximately a quarter of the wavelength of an input signal having a frequency at a lowest limit and the other has a length of approximately a quarter of the wavelength of an input signal having a frequency at an uppermost limit.
(6) one end each of a first series resonance circuit and a second series resonance circuit comprising an inductor and a capacitor in series is to be connected to the gate of FET, and the respective other ends are to be grounded. Moreover, either one of resonance frequencies of the first series resonance circuit or the second series resonance circuit is made approximately twice the wavelength of an input signal having a frequency at a lowest limit and the other has a length of approximately twice the wavelength of an input signal having a frequency at an uppermost limit.
However, the following problems existed in forming a transmission or resonance circuit for purpose of eliminating distortion in the high-frequency power amplifier circuit:
(a) The length of the transmission line requires at least one eighth of the wavelength of the input signal. Due to this, miniaturization is hampered when the high-frequency power amplifier circuit is configured as a module.
For example, the length of transmission line will become approximately 12.5 mm when the high-frequency power amplifier circuit with the frequency of the input signal being 1 GHz is formed on an alumina substrate (.epsilon.=9.6). Therefore, it becomes difficult to proceed with formation onto a substrate of the aforementioned conventional example, and thus the demand for the miniaturization cannot be complied with.
(b) A plurality of resonance circuits must be provided for applicability to a plurality of higher harmonic components since it is necessary to set up resonance frequencies of the resonance circuit so as to correspond with respective higher harmonic wave of input signal frequencies. Moreover, the miniaturization of a circuit and a device is hampered since also for noise component other than higher harmonic component resonance circuits must be provided respectively.